1. Field of the Invention
This invention relates to a high performance semiconductor component provided with a casing in which a semiconductor disk having at least one pn-junction is material-connected with a metal disk, serving for heat conduction and for current supply, through numerous conductors forming a brush-like bundle wherein the conductors are material connected at one of their ends only with the semiconductor disk but not with each other.
2. Description of the Prior Art
Such a high performance semiconductor component is known from the German Patent Application P 28 55 493.0. The individual wires are embedded in silicone rubber and twisted in such a fashion that the outside wires are longer than the inside ones. Since the copper disk material-connected with the one end of the wire brush, i.e. by means of soldering, welding or diffusion-bonding, expands more when heated than the silicon disk material-connected with the other end of the wire brush, the outside individual wires must compensate for a larger radial difference in length than those which are further inside. When compensating for the radial differences in length, the twisting of the individual wires is partially eliminated, i.e. the length running in tangential direction is partially converted into a length running in radial direction whereby the distance between semiconductor disk and copper disk remains the same.
A spring contact element is known from the British Pat. 876,133 which consists of a spirally wound, slotted copper tape which bulges out in the area of the longitudinal slots. The wound copper tape spiral is held together at its upper and lower ends by a put-on cap and a soldered-on cap. One of the two caps is soldered to a metallic counter-electrode and this counter electrode, in its turn, to the semiconductor disk. Thus, the known contact element can only compensate for axial thermal expansion differences; radial thermal expansion differences are compensated for by the metal electrode soldered between cap and semiconductor disk. For this reason, the known semiconductor component can only be used for relatively low performances.
A largely solder-free contacting of a semiconductor disk with the outer connecting contacts is known from the German Disclosure Publication 15 14 149. For this purpose, a so-called multi-contact cushion which consists of a fine-wired, felt-like metal blank is pressed on the semiconductor disk. This is thus a special form of pressure contacting. Since the silicon disk expands by far less in radial direction when heated than the copper contact disk or the multi-contact cushion, respectively, the outer wires of the multi-contact cushion must slide on the surface of the silicon disk. Therefore, the application is not possible for large-area semiconductor components.
Since it has been determined in the past that soldered connections with semiconductor disks are only usable when the semiconductor disks do not exceed a certain diameter, the pressure contact technique has been generally applied for high performance semiconductor components with large-area silicon disks. The construction of such a pressure-coated semiconductor component is known, for example, from "IEEE Transactions on Electron Devices", Vol. Ed-26, No. 7, July 1979, pages 1085-1091. An essential characteristic of pressure-coated semiconductor components is the use of a molybdenum disk and/or a tungsten disk between a silicon disk and a copper disk serving as a heat reduction. Molybdenum and tungsten have thermal expansion coefficients which are similar to that of silicon. In this way, the surface of the silicon disk is exposed to little mechanical stress with thermal expansions. A disadvantage of this generally applied pressure contact technique is the low thermal conductivity of tungsten, and particularly molybdenum, as well as the bad contact which exists only at a few points between the silicon and tungsten or molybdenum disks. This point contact which exists only at a few places leads to an additional reduction in the heat conduction from the silicon disk as well as to a concentration of the electrical current on these few contact points. The authors of the above-noted literature reference come to the conclusion, on the basis of theoretical considerations and practical investigations, that the surge current resistance of a given silicon tablet could be increased by approximately 50% and the continuous direct current resistance by approximately 90% by eliminating the point contacts between the silicon disk and the metal disks resting on top and between the metal disks among themselves. Further dramatic improvements could be reached if one would succeed in replacing the tungsten and molybdenum disks by copper cooling bodies. However, it is also pointed out that the thermal-mechanical problems occurring in this instance, such as the grating of the silicon disk on parts of the casing or the hardening of the soldered connections, could not be controlled with the customary means.